1. Field of the Invention
This invention relates to a method of generating seismic signals for use in geophysical mapping and prospecting. The method employs a projectile firing gun and includes means of improving the transfer of energy from the projectile to the earth's surface to enhance the amplitude and quality of the seismic signal generated.
2. Description of the Prior Art
A variety of different means of generating seismic signals have been known and practiced in the art such as vibrators, dynamite, detonating cord, air guns and weight drop units. The referenced parent application provides a unique arrangement for generating seismic signals in which a projectile is fired into the earth. The impact of the projectile generates a seismic signal. Reflections from the seismic signals detected by geophones positioned on the earth can be used to provide information as to the depth and contour of subterranean stratas.
When using the seismic energy signal method and apparatus of the referenced parent application, the quality and amplitude of the signal is determined by the nature of the surface of the earth at the point of the projectile impact. The characteristics of the earth's surface varies substantially from one position to another. Some spots on the earth are very hard, consisting of layers of exposed rock. Other areas are spongy, such as areas high in vegetable matter content. Even at the same location, weather conditions can change the characteristic of the earth's surface. For instance, if the surface is frozen, the nature of the impact of a projectile is completely different from the same spot under high temperature conditions wherein the spot may be either relatively dry but unfrozen or may be spongy or substantially saturated with water.
A particular problem is encountered when a spongy type surface exists such as a surface having lush vegetation. The impact of the fired projectile is absorbed over a longer stretch of time compared with the impact of a hard surface, and therefore, the amplitude of the seismic signal is substantially diminished. In addition, the characteristic of the signal is affected.
The present invention is directed towards a method of generating a seismic signal and of seismic exploration utilizing such generated seismic signal, including means of improving the amplitude and quality of seismic signals obtained from a fired projectile.
It is therefore an object of this invention to provide an improved method of generating a seismic signal and improved means of seismic exploration utilizing such improved signals.
More particularly, an object of this invention is to provide a method of generating a seismic signal in which the nature of the surface of the earth at the point where a projectile is to be fired into the earth can be altered in an expeditious manner to thereby create seismic signals of greater amplitude and more uniform character.
These general objects as well as other and more specific objects of the invention will be fulfilled in the following description and claims, taken in conjunction with the attached drawings.